We report on the observation of optical quenching of persistent photoconductivity (PPC) in unintentionally doped n-type GaN films. The PPC is induced by subbandgap illumination between room temperature and 77K. The corresponding decay, which.is thermally activated, is substantially increased upon low energy illumination, e.g. illumination by wavelengths between 1O50nm and 700nm. We measure the saturation conductivity under simultaneous illumination with excitation and quenching light and find that some wavelengths can induce both excitation and quenching of photoconductivity. Additionally, we present a preliminary investigation of the spectral dependence of the quenching effect. A simulation indicates only a weak spectral dependence of the quenching cross-sections in the wavelength range from 470nm–1050nm.